SkeletalSystem2MicroscopicAnatomy

Bio230Dr.CarlaSweet

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(b)Endosteum

Osteoprogenitorcell

Osteoblasts

Osteoclast

Bonematrix

Canaliculi

Endosteum

Osteocyteinlacuna

Osteoid

Perforatingfibers

Circumferentiallamellae

Periosteum

(a)Periosteum

Endosteum

PeriosteumCompactbone

Osteocyteinlacuna

Canaliculi

Cellularlayer

Fibrouslayer

(akaVolkmann’scanal)

MicroscopicAnatomyofbone.Osteon (akaHaversian system)=thestructuralunitofcompactbone.

Thisfigureshowsasingleosteondrawnasifpulledoutlikeatelescopetoillustratetheindividuallamallae.

Thispatternofalternatingthedirectionofcollagenfibersineachlamellaegivesboneaddedstrengthtoresisttorsionstresses.

MicroscopicAnatomy-anotherview

P

NerveConcentriclamellae Vein Artery

Canaliculi

Centralcanal

Osteon

Lacuna

CollagenfiberorientationCentralcanal

Osteon

Externalcircumferential

lamellae

Perforatingfibers

Periosteum

Fibrouslayer

Cellularlayer

Osteocyte

CanaliculiInterstitiallamellae

Trabeculaeofspongybone

Endosteum

Osteoclast

Parallellamellae

Osteocyteinlacuna

Osteoblastsalignedalongtrabeculaofnewbone

Canaliculiopeningatsurface

Perforatingcanals

Centralcanal

Trabeculae

Spaceforbonemarrow

Interstitiallamellae

Puttingitalltogether!

Histology:Groundbonepreparation:hard(compact)bonesampleisgrounddown.Thistypeofpreparationdestroyslivingcells,howeverdetailsoftheboneymatrixarepreserved.

OsteonsFoundonlyinCompactbone

Bone:Ossification/OsteogenesisBeforeweek8theskeletonofthehumanembryoconsistsonlyofhyalinecartilageandsomemembranesofmesenchyme (embryonictissue-stemcells).After8weeksbonetissuestartsappearingandreplacesmostcartilageandmesenchymal membraneintheskeleton.

2typesofBoneFormation:1. Intramembranous ossification:

Herebonedevelopsfrommesenchymal membrane.Thesearetheflatbonesoftheskullandtheclavicles(collarbone).Inthisprocessmesenchymal cellsclusteranddifferentiateintoosteoblastswhichstartmakingbonematrix.

2.Endochondral Ossification:“endo”=within”“chondra”=cartilage.Inthisprocessbonesdevelopashyalinecartilageisreplacedwithbone.Mostofourbonesareformedinthismanner.Endochondral ossificationstartsat8weeksinfetaldevelopmentandisnotcompletedtillearlyadulthood.

embryovs.fetus:Fetus:Theunbornoffspringfromtheendofthe8th weekafterconception(whenthemajorstructures

haveformed)untilbirth.Upuntiltheeighthweek,thedevelopingoffspringiscalledanembryo.

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EndochondralOssification

Deterioratingcartilagematrix Epiphyseal

capillaries

Epiphysealbloodvessel

Epiphysealplate

Articularcartilage

Spongybone

Medullarycavity

Compactbone

Periosteum

Epiphysealplatesossifyandformepiphyseallines.

Spongybone

Epiphysealline

Articularcartilage

Bonereplacescartilage,exceptthearticularcartilageandepiphysealplates.

Epiphysealplate

Perichondrium

Developingperiosteum

Fetalhyalinecartilagemodeldevelops. Cartilagecalcifies,

andaperiostealbonecollarformsarounddiaphysis.

Secondaryossificationcentersforminepiphyses.

Primaryossificationcenterformsinthediaphysis.

Calcifiedcartilage

Developingcompactbone

Medullarycavity

Secondaryossificationcenters

PrimaryossificationcenterBlood

vesselofperiostealbud

Periostealbonecollar

Hyalinecartilage

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Epiphysealline(remnantofepiphysealplate)

Endochondral Ossificationprocessbelow

Hyalinecartilagereplacedwithbone=Endochondral Ossification

Endochondral (insideCartilagemodel)BoneDevelopment

BesureyoucanIDeachofthesezonesonaslide

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restingproliferatinghypertrophycartilagecalcificationosification

The5zonesofEndochondral ossification:Hyalinecartilagereplacedbybone

noticethesizeofosteoblasts comparedtoosteoclasts.Whatdoosteoblasts do?Whatdoosteoclasts do?

intramembranous ossification : boneformswithinamesenchymal membrane

(Bone)